Conventionally, an automatic tensioner has been used in order to adjust the tensile force of a timing belt or an auxiliary machine driving belt used in a car engine, and the thus-adjustable belt has been used to drive an auxiliary machine such as a compressor. And, in a rotation support part for a pulley for use in the automatic tensioner or a driven pulley for driving the above auxiliary machine, there is supported such pulley on a fixed part using a rolling bearing in such a manner that the pulley can be rotated with respect to the fixed part.
For example, FIG. 32 shows a first example of conventional structures in which a double-row rolling element bearing is used in the rotation support part of a compressor to be incorporated into a car air conditioner to thereby compress a refrigerant. A rotary shaft 1 of this compressor is rotatably supported within a case 2 by a rolling bearing (not shown). On the periphery of a support tube part 3 formed in the outer surface of the end portion of the casing 2 and corresponding to a support part as set forth in the appended claims, there is rotatably supported a driven pulley 4 using a double-row radial ball bearing 5. The driven pulley 4 is structured such that it has a U-shaped section and it is formed in a circular-ring shape as a whole; and, a solenoid 6 fixed to the end face of the casing 2 is disposed in the internal space of the driven pulley 4. On the other hand, to the portion of the end portion of the above rotary shaft 1 that is projected from the above casing 2, there is fixed a mounting bracket 7; and, on the periphery of this mounting bracket 7, there is supported a ring-shaped plate 8 made of magnetic material through a plate spring 9. The ring-shaped plate 8, when the solenoid 6 is not energized electrically, is separated a part from the above driven pulley 4 due to the elastic force of the plate spring 9, as shown in FIG. 32; and, on the other hand, when the solenoid 6 is energized, the ring-shaped plate 8 is attracted toward this driven pulley 4 to be thereby be able to transmit the rotation power from this driven pulley 4 to the above rotary shaft 1. That is, the solenoid 6, ring-shaped plate 8 and plate spring 9 cooperate together in constituting an electromagnetic clutch 10 which is used to engage the above driven pulley 4 and the above rotary shaft 1 with each other and disengage them from each other.
According to the above-mentioned structure in which the driven pulley 4 is rotatably supported using the double-row radial ball bearing 5, even in case where a small level of partial load is applied to this driven pulley 4 from an endless belt 11 provided on this driven pulley 4, there is little possibility that the center axes of an outer ring 12 and an inner ring 13 respectively constituting the above double-row radial ball bearing 5 can be incongruous with each other (can be inclined with respect to each other). Therefore, not only the durability of the above double-row radial ball bearing 5 can be secured sufficiently but also the rotation center of the above driven pulley 4 can be prevented against inclination, thereby being able to prevent the above endless belt 11 against partial wear.
However, use of the above double-row radial ball bearing 5 inevitably increases the axial-direction dimension of the above structure. The rotation support part of the above driven pulley 4, in many cases, must be disposed in a limited space and thus the increase in the axial-direction dimension is not desirable. Also, the increase in the axial-dimension increases the costs of the composing parts of the structure.
In case where, as a rolling bearing for supporting the above driven pulley 4, instead of the above double-row radial ball bearing 5, there is used a single-row deep-groove-type radial ball bearing, the axial-direction dimension of the structure can be reduced to thereby be able to facilitate the installation of the rotation support part of the bearing in a limited space. However, in the case of a simple single-row deep-groove-type radial ball bearing, when a moment load is applied to the above driven pulley 4, there is obtained a small force to prevent the inclination of this driven pulley 4, which greatly increases the degree of incongruity between the center axes of the outer and inner rings respectively constituting the above radial ball bearing. As a result of this, not only the durability of the above radial ball bearing is insufficient but also great partial wear is easy to occur in the endless belt 11 arranged on the above driven pulley 4.
In view of the above circumstances, conventionally, there are proposed structures, as disclosed in the following patent reference 1 and patent reference 2, in which a single-row four-point-contact-type radial ball bearing is used to support a driven pulley. Here, FIGS. 33 and 34 shows a second example of the conventional structures disclosed in the patent reference 1.
According to the second example of the conventional structures, a driven pulley 4a, which is formed by enforcing a bending working operation such as a press working operation on a metal plate, can be rotatably supported on the periphery of a support part (not shown) using a single-row four-point-contact-type radial ball bearing 14. This radial ball bearing 14 comprises an outer ring 15 and an inner ring 16 supported so as to be concentric with each other, and two or more rolling elements 17, 17. Of these composing elements, in the inner peripheral surface of the outer ring 15, there is formed an outer raceway 16 and, in the outer peripheral surface of the inner ring 15, there is formed an inner raceway 19 in such a manner that they respectively extend over the entire peripheries of their associated peripheral surfaces. The section shapes of the respective raceways 18 and 19 are respectively so called Gothic arch shapes in which two arcs each having a radius of curvature larger than one half of the diameters of the respective rolling elements 17, 17. Therefore, the respective raceways 18, 19 and the rolling surfaces of the respective rolling elements 17, 17 are contacted with each other respectively at two points, that is, at a total of four points in every rolling elements 17, 17.
The thus-structured four-point-contact-type radial ball bearing 14 is large in rigidity with respect to the moment load when compared with an ordinary single-row deep-groove-type radial ball bearing and, even when the moment load is applied thereto, the center axes of the outer ring 15 and inner ring 16 are difficult to shift from each other. Thanks to this, when compared with a structure in which a pulley rotation support device for a compressor is formed using an ordinary single-row deep-groove-type radial ball bearing, there can be eased the partial wear that occurs in the endless belt 11 (see FIG. 32) arranged on the driven pulley 4. By the way, in the patent reference 2, there is disclosed a structure in which the above-structured four-point-contact-type radial ball bearing is assembled to the rotation support part of a driven pulley for driving a compressor and further, between the driven pulley and the rotary shaft of the compressor, there is interposed an electromagnetic clutch.
Also, in the case of such a single-row three-point-contact-type rolling element bearing 14a as shown in FIG. 35 as well, it has larger rigidity with respect to the moment load than an ordinary single-row deep-groove-type radial ball bearing and thus, even when it receives the moment load, the center axes of an outer ring 15 and inner ring 16a are difficult to shift from each other. According to the single-row three-point-contact-type rolling element bearing 14a, in the outer peripheral surface of the inner ring 16a, there is formed an arc-shaped inner raceway 19a, whose section to be contacted with the rolling surface of the rolling element 17 at a point has a single curvature; and, in the inner peripheral surface of the outer ring 15, similarly to the four-point-contact-type radial ball bearing 14 shown in the above-illustrated FIGS. 33 and 34, there is formed a Gothic-arch-shaped outer raceway 18 which is to be contacted with the rolling surface of the rolling element 17 at two points. In the structure in which a pulley for a compressor is supported using the thus-formed three-point-contact-type rolling element bearing 14a, when compared with the structure in which a pulley rotation support device for a compressor is formed using an ordinary single-row deep-groove-type radial ball bearing, there can be eased the partial wear that occurs in the endless belt 11 (see FIG. 32) provided on the driven pulley 4. A similar effect can also be obtained in a three-point-contact-type rolling element bearing having a structure in which, contrary to the structure shown in FIG. 5, the rolling surfaces of the respective rolling elements are contacted with an outer raceway at a point and are contacted with an inner raceway at two points.
As described above, when the above-mentioned three-point-contact-type or four-point-contact-type radial ball bearing is assembled to the rotation support part of the pulley, there is a possibility that the reduction in the size and weight of the structure and the durability thereof are compatible with each other on a high level. However, in the case of the conventional structures, since the factors and elements of the respective parts thereof are not examined to the full, there cannot be always obtained a sufficient effect.
Also, in the case of an auxiliary machine for an engine, especially, in the case of a compressor, recently, there have been made improvements such as an increase in the rotation thereof, an increase in the capacity thereof, and a decrease in the axial-direction dimension thereof. However, when the auxiliary machine is improved in the rotation thereof and the like, a rolling element bearing for supporting a pulley for the auxiliary machine is easy to generate heat, which reduces the seizure life (deterioration life) of grease. Also, since an excessively large moment load is applied to the rolling element bearing, the rolling elements are easy to run up onto the shoulder portions of an outer raceway and an inner raceway. Further, in the case of other machines than the auxiliary machines of the engine, for example, in the case of an automatic tensioner as well, when an increase in the rotation thereof or a reduction in the axial-direction dimension is required, in a rolling element bearing for supporting a pulley which is used in such machine, similarly, the seizure life of grease can be shortened or the rolling elements are easy to run up onto the shoulder portions of the outer raceway and inner raceway. Therefore, in a rolling element bearing to be used in the machine such as an engine auxiliary machine which is required for an increase in the rotation and capacity thereof as well as is required for a reduction in the size thereof, when no consideration is given at all to an increase in the seizure life of the grease and a run-up allowance of the rolling element (a ratio which expresses the difficulty for the rolling element to run up onto the shoulders of the raceways), there is a possibility that these performances of the rolling element bearing can be insufficient. By the way, in case where the seizure life of the grease is sufficiently long, since the life of the bearing is determined by the rolling fatigue lives of the inner ring and outer raceways, to enhance the seizure life of the grease is not specially important. However, in case where the seizure life is not long so much, because there is a possibility that the bearing life can be determined by this seizure life, from the viewpoint of securing the bearing life, to enhance the seizure life is especially important.
In view of the above circumstances of the conventional pulley rotation support apparatus, according to the invention, there is provided a pulley rotation support apparatus which not only can secure the durability of a rolling bearing and an endless belt arranged on a pulley but also, even when it is used in a machine required for an increase in the rotation and capacity thereof as well as for a reduction in the size thereof, can fully secure the seizure life of grease to be charged into the interior of the rolling bearing as well as the run-up allowance of a rolling element.
Patent Reference 1
    JP-A-9-119510Patent Reference 2    JP-A-11-336795Patent Reference 3    JP-A-11-210619Patent Reference 4    JP-UM-A-64-27482